A surgical microscope of the kind referred to above is manufactured and sold by Carl Zeiss Surgical GmbH under the designation OPMI® Pentero™. This surgical microscope is designed for neurosurgery and has an illuminating arrangement for illuminating the operating region or region of surgery with a 300 watt xenon high-power light source. The intensity of the illuminating light, which is made available by the illuminating arrangement, can be adjusted quasi-continuously with a filter diaphragm between a minimum value and a maximum value. The surgical microscope makes possible a visualization of the regions of surgery with fluorescence light in the infrared and blue spectral range.
It is necessary to illuminate well the finest tissue structures in order to make them visible with a surgical microscope. This requires a power intense illuminating arrangement in the surgical microscope. In the illuminating arrangements of surgical microscopes for neurosurgery and HNO-surgery, high-power light sources are therefore used. Illuminating light, which is guided to an operating region, interacts, however, with body tissue. This leads especially to warming and can, for the case that the illuminating intensity is too high, cause persistent damage to tissue structures even when the ultraviolet and infrared light, which is outputted by the high-power light source, is filtered out.
In order to be able to optimally adjust a surgical microscope for a surgical procedure, it is advantageous when the surgeon has the possibility to vary especially the intensity and spectral composition but also the size of the illuminated area of the illuminating light as well as the working distance of the surgical microscope with reference to the object region. The illuminating light is generated with the illuminating arrangement in the surgical microscope.